This invention generally deals with television camera picture reproduction and deals more particularly with a system for synchronizing the operation of a lens shutter apparatus with ordinary synchronizing signals conventionally employed in television picture generation, to allow faithful, high clarity picture reproduction of scene objects traveling at relatively high rates of speed across the camera's field of view.
Television systems in the United States utilize a picture frame comprising 525 horizontal lines of image data interlaced to form a pair of superimposed picture fields, each field consisting of 2621/2 lines. Each field is scanned in 1/60 of a second so that a single picture frame (consisting of a pair of interlaced fields) is scanned in 1/30 of a second. Thus, the light of the scene object is successively focused on the camera's pickup tube for periods of 1/60 of a second. In the case of scene objects relatively distant from the camera's lens which are moving across the latter's field of view at relatively high rates of speed, movement of the image of the scene object focused on the pickup tube is minimal and a relatively clear picture of the scene object may be formed within the 1/60 of a second available for scanning. However, where the scene object is only a few feet away from the camera's lens and is traversing the latter's field of view at relatively high rates of speed, the movement of the image focused on the pickup tube is rather substantial within the 1/60 second interval, resulting in the reproduction of a blurred picture image. Heretofore, because of the above-mentioned deficiency, there has been minimal demand for televising scene objects moving rapidly across the camera's field of view, however, with the expanding role of television in commercial settings, a need has been created for high speed, television camera operation. One typical commercial application of television systems benefiting from the present invention involves the use of television cameras to visually "read" identification data imprinted on the sides of railroad cars. In this application, the camera is stationarily mounted immediately adjacent to the train of cars and transmits a televised image of the data associated with each car as the latter traverses the camera's field of view. The televised identification data is transmitted to a remote location and is used in sorting, spotting and scheduling the railroad cars. In the past, however, due to the operational limitations inherent in prior art conventional television cameras, the railroad cars were required to be drawn past the camera's field of view at very slow rates of speed, e.g. less than 10 miles per hour, thus requiring in many instances that the train be slowed to the required speed when passing the camera installation. With the aid of the present invention however, existing television cameras may be adapted to faithfully reproduce pictures of the identification data without a loss of clarity, with railroad cars moving at speeds in excess of 100 miles per hour. In fact, the present invention enables a conventional black and white or color television camera, for the first time, to reproduce clear pictures of proximal objects moving at speeds in excess of 200 miles per hour.
Conventional television cameras employ any of several types of signal timing circuits for synchronizing the scanning of the camera's pickup tube with the generation of television pictures, including: internal circuits having free-running or crystal controlled oscillators; external circuits driven by external sync-pulse generators; and, line-lock type circuits which include an internal oscillator that derives its time base from the frequency of an alternating current power source (typically 60 Hertz in the U.S.). In the past, others have attempted to improve picture clarity by adapting shutter apparatus for use with a television camera having timing circuitry of the line-locked type; the shutter apparatus was driven by an alternating current motor coupled with commercial electrical power service so that the shutter apparatus operated at approximately the same rate as the camera's picture generation system. The operation of this previous system was less than satisfactory since various factors, including mechanical error inherent in such a system, prevented precise synchronization of the shutter opening with pickup tube scanning, especially when high shutter speeds were required consequently, picture quality in these known prior systems were less than desired. In any event, none of the known prior attempts at providing a high speed television camera system have successfully employed cameras having internal or external timing circuits of the mentioned types.
The present invention overcomes the above discussed deficiencies inherent in prior art designs by providing a rotating shutter device disposed in the optical path of the pickup tube of a conventional television camera which is driven by an electronically controlled motor in synchronization with the scanning of the camera's pickup tube to successively expose the latter to scene objects for prescribed timed intervals in order to allow clear reproduction of fast moving objects by "stopping" the action of the latter. The invention is adapted for use with several common varieties of camera systems including power-line locked, externally synchronized, and internally synchronized types (employing free-running oscillators) all of which employ common synchronizing signals for generating television pictures. Control circuitry is provided for receiving the picture synchronizing signals and conditioning the same for use as motor driving signals. The motor driving signals are delivered to a pair of novel motor driving amplifiers whose energizing outputs are transformer coupled to the shutter motor and function to control the speed and phase of the latter in order to synchronize the operation of the shutter device with the scanning of the pickup tube to assure high clarity picture reproduction. A photodiode and a phototransistor cooperate with the shutter device to product a tachometer signal indicative of the speed and phase positioning of the shutter, which is fed back to the motor driving amplifiers to provide automatic, initial adjustment of the phase position of the shutter device after start-up of the system.
An important object of the invention is to provide unique apparatus and a novel method for selectively exposing one or more pickup tubes of a conventional television camara to fast moving scene objects in order to permit clear, accurate picture reproduction of the latter.
Another primary object of the invention is to provide a novel control circuit for detecting certain timing signals produced by a sync-pulse generator used in a conventional television system, and for conditioning the detected signals for use in controlling the operation of an electrical motor device in order to precisely synchronize the operation of the latter with the scanning operation in said television system.
A further object of the invention is to provide novel control circuitry for synchronizing the operation of shutter apparatus associated with the lens of an ordinary television camera with the scanning of the latter's pickup tube in order to insure coordinated cooperation of the scanning and exposure functions for television reproduction of high speed scene objects.
A still further object of the invention is to provide unique apparatus and circuitry of the type described which includes a shutter driving motor responsive to drive the shutter in accordance with the production of picture synchronizing signals, whereby to synchronize the operation of shutter apparatus with the scanning of the camera's pickup tube. As a corollary of the foregoing object, it is a further object to provide apparatus and circuitry of the mentioned type wherein tachometer means associated with the operation of the shutter apparatus is operative to produce a feedback control signal which is used for correcting the phase of the motor and the shutter apparatus.
Another object of the invention is to provide electronic control system circuitry which is operative to receive any of a number of conventional types of pictures scanning synchronizing signals and condition the received signals in accordance with the feedback control signal to produce the motor driving control signal for controlling the speed as well as phase of the motor and shutter apparatus. An object related to the foregoing object, is to provide means for comparing the phase of a feedback signal with that of the received synchronizing signal and correcting the phase of the latter in accordance with the phase of the former.
A further object of the present invention is to provide electronic control circuitry of the mentioned type which employs a pair of motor driving amplifiers respectively responsive to input control signals for transformer coupling energizing power to the shutter driving motor.
A still further object of the invention is to provide a novel method for eliminating the undesirable effects of image carryover between successively scanned picture fields in a conventional television camera due to image retentivity of the latter's image pickup tube.
Other and further objects of the invention will be made clear or become apparent in the course of the following description of a preferred embodiment of the invention.